Methionine uptake and excretion in Corynebacterium glutamicum. The characterization of methionine uptake in C. glutamicum revealed two uptake systems. The first system is a high-affinity transporter with a Km of ~ 0.1 µM and a Vmax of ~ 0.7 nmol/min (mg dw). Data base searches with the E. coli methionine uptake system MetD as query resulted in the identification of the genes metI, metN and metQ in C. glutamicum. The expression of this gene cluster encoding an ABC transporter is regulated by the repressor McbR. The second uptake system is a medium-affinity transporter with a Km of ~ 88 µM and a Vmax of ~ 1.65 nmol/min (mg dw). This transport system, named MetP according to its E. coli counterpart was characterized in detail in the metNI deletion strain. Because of its sodium dependency MetP is a secondary active transporter, which is inhibited by the addition of alanine, valine, isoleucine, leucine and cystein. Furthermore, metP does not belong to the McbR regulon. To characterize methionine export, an L-methionine containing dipeptide loading system was established. The dipeptide is taken up by the cell and hydrolyzed in the cytoplasm, resulting in a strong increase of the internal methionine concentration. Afterwards the internal concentration decreased. It was shown that BrnFE is the main export system for methionine, whereas the expression of brnFE depends on the cytoplasmic methionine concentration. Since there was methionine export detectable in the brnE deletion strain, a further export system was expected. Cgl0944, identified by DEUTENBERG (2003) in a gene expression analysis, could be excluded as a methionine export system. Investigations presented in this work indicate, that the further export system is not of secondary type and its activity is influenced by the external osmolality. Its corresponding gene is not regulated on the level of gene expression. Furthermore, in this work the existence of extracellular membrane-bound or cell surface-attached hydrolases that cleave dipeptides, was proven.